Using miniaturised hooks and bobbins single DNA strands can be manoeuvred without breakage. (Credit: Image courtesy of Royal Society of Chemistry)

(Click image to enlarge)

Japanese scientists have made a micro-sized sewing machine to sew long
threads of DNA into shape. The new work demonstrates a unique way to
manipulate delicate DNA chains without breaking them.

Scientists can diagnose genetic disorders such as Down's syndrome by
using gene markers, or "probes", which bind to only highly similar
chains of DNA. Once bound, the probe's location can be easily detected
by fluorescence, and this gives information about the gene problem.

Detecting these probes is often a slow and difficult process,
however, as the chains become tightly coiled. The new method presented
by Kyohei Terao from Kyoto University, and colleagues from The
University of Tokyo, uses micron-sized hooks controlled by lasers to
catch and straighten a DNA strand with excellent precision and care.

"When a DNA molecule is manipulated and straightened by microhooks
and bobbins, the gene location can be determined easily with
high-spatial resolution," says Terao.

The team use optical tweezers - tightly focused laser beams - to
control the Z-shaped micro hook and pick up a single DNA "thread". The
hook is barbed like an arrow, so the thread can't escape. When caught
on the hook, the DNA can be accurately moved around by refocusing the
lasers to new positions.

But just like thread in a sewing machine, a long DNA chain can be
unwieldy - so the researchers built micro "bobbins" to wind the chain
around. The lasers move one bobbin around another, winding the DNA
thread onto a manageable spindle.

It is "an excellent idea to fabricate unique microtools that enables
us to manipulate a single giant DNA molecule", says Yoshinobu Baba, who
researches biologically useful microdevices at Nagoya University,
Japan. The technology will also be useful for a number of other
applications including DNA sequencing and molecular electronics, he
adds.